It has been discovered by others that an isotope of iodine, i.e., .sup.125 I, may be tagged on to the chloroquine so that, upon introduction to the human body, the chloroquine is absorbed into the body tissue with the .sup.125 I label intact. It has also been discovered by others that the chloroquine is absorbed at a greater rate in melanotic tumors such as active melanomas of the eye. Accordingly, the type of absorbed abnormality, i.e., malignant melanoma versus hemangioma or other benign condition can be determined by measuring the concentration of chloroquine. Since the concentration of chloroquine is related to the presence of the associated isotope of iodine, an ionizing radiation detector which measures the ionizing radiation emitted by the isotope of iodine, and hence the concentration of the isotope of iodine and chloroquine, serves as an indication of the type of observed anatomical abnormality.
It has also been discovered by others that an ultrasound chart or "picture" of a body portion such as the eye can be constructed using an ultrasound probe by emitting ultrasound energy along a defined axis and displaying the returned portion of the ultrasonic energy in the time domain. Abnormalities in the body or other abrupt changes in the body structure causes the return of a portion of ultrasonic energy so that a display of the returned ultrasonic energy in the time domain portrays the location of these changes or abnormalities along the defined axis. By movement of the defined axis through a portion of the body, either by translational displacement or rotational displacement, an ultrasound chart or picture of that body portion can be displayed.
The present invention combines the two aforedescribed technologies in a unique way which permits accurate three-dimensional location of a radiation detecting probe with respect to the abnormality by guiding the radiation detecting probe using an ultrasound probe and an ultrasound signal display system. The advantages of the present invention will be best appreciated if prior methods and apparatus for detecting abnormalities using a radiation detecting probe are considered.
One prior art method for determining the existence of an ocular melanoma is to introduce the isotope carrying chloroquine to the body so that it may be absorbed by the tissue in each eye of the patent. An uncollimated radiation detector measures the radiation emitted by each eye of the patient, for example, by counting the emission of ionizing radiation. The count differential between the respective eyes is used as an indication and measure of any abnormality. However, the standard deviation between two normal eyes, i.e., eyes which have no abnormalities, is substantial thereby leading to inconclusive results, particularly in the case of smaller tumors. Furthermore, the radiation is detected over a background level radiation emitted by the entire chloroquine absorbing tissue. The background radiation can readily mask small tumors thereby further reducing the sensitivity of this prior art method. The sensitivity of this prior art method is also reduced by variations in the probe placement.
Another prior art method of detecting ocular melanomas involves a surgical procedure in which the conjunctiva is incised, the eye rotated in its socket, and thereafter, the radiation detecting probe is accurately placed directly over the suspected tumor by a surgeon. Positioning is accomplished by visual means. In addition to this prior art method's drawback of requiring a surgical procedure, this prior art method still has the disadvantage of the above described method in that a substantial level of background radiation exists which masks the radiation from the area of interest. Furthermore, opaque eyes add additional complications in visual aiming of the detector.
Accurate positioning of a radiation detection probe relative to various anatomical features is useful for organs other than the eye and for radio-labelled compounds other than the chloroquine. Here, prior art methods for positioning may also include knowledge of anatomy and/or palpation or even sequential positioning (scanning) over whole areas of the body.
The present invention overcomes the disadvantages of the prior art methods and apparatus for locating sources of ionizing radiation, such as body abnormalities, by providing a radiation detector which has maximum responsiveness or sensitivity to radiation emitted from a restricted small volume in combination with an ultrasound guidance system for accurately placing the small volume of greatest sensitivity of the radiation detecting probe at a suspected abnormality. More specifically, the radiation detecting probe is provided with a focusing collimator which generally restricts the sensitivity of the probe to a small defined volume and is guided by an ultrasound probe so that the restricted volume may be located at a suspected abnormality. The ultrasound guidance system includes an ultrasound probe which emits a focused beam of ultrasonic energy along a first axis which coincides with the focal point of the collimator. The ultrasound guidance system further includes a signal processing system which detects and displays in the time domain any portion of the outgoing ultrasonic energy which is returned to the ultrasound probe. Ultrasonic energy is returned to the ultrasound probe when it strikes a body portion or substance of differing acoustic transmission. One such portion of different acoustic transmission would be a body abnormality such as a tumor, e.g., an ocular melanoma. By sweeping or displacing the ultrasound probe through an area of the body, and simultaneously or subsequently displaying the returned ultrasonic energy in the time domain, a chart or pattern can be constructed which indicates the location of portions of differing acoustic transmission. This display or indication can be used as a preliminary indicator of a suspected abnormality.
The collimated radiation detector is positioned relative to the ultrasound probe so that the focal point of the detector collimator will coincide, or substantially coincide, with either the focal point or the focal axis of the ultrasound probe. Preferably, the ultrasound display system is provided with a range marker which indicates on the display the location of the coincidence of the focal point of the radiation detecting probe and the axis of the ultrasound probe on the ultrasound display. By this means, the radiation detecting probe can be moved so that the focal point of its collimator is positioned at the suspected abnormality. Once it is so positioned, a radiation count of the emissions from the suspected abnormality can be made. After that radiation count is made, the radiation detecting probe can be moved to locate the focal point of its collimator in normal tissue so that a background or reference radiation count can be made. The difference in the radiation counts is an indication of specificity of the abnormality for the uptake of the particular radio-labelled compound employed.
The range marking system may provide a plurality or range marks. For example, three range marks can be generated, a first at the coincidence of the focal point of the radiation detecting probe collimator and the axis of the ultrasound probe, a second space a predetermined distance from the coincidence mark along either the axis of the ultrasound probe or, if the configuration is such that the axis of the radiation detecting probe lies in the plane of the ultrasound imagine, i.e., the x-theta plane (described hereinafter), the axis of the radiation detecting probe, and a third also spaced a predetermined distance from the coincidence mark along either the axis of the ultrasound probe or the axis of the radiation detecting probe, but on the opposite side of the coincidence mark.
In the preferred embodiment, the range marker system includes a timer which is activated upon emission of the ultrasonic pulse by the ultrasound probe and introduces a substantial pulse simulating a returned ultrasonic pulse at a time corresponding to the return time of a pulse reflecting from the coincidence point. In the embodiment providing two additional range marks, two additional pulses are provided, one occurring at the return time of a pulse reflecting from a predetermined distance short of the coincidence point, and another occurring at the return time of a pulse reflecting from a predetermined distance on the opposite side of the coincidence point.
In view of the above discussion, and the detailed description of the preferred embodiment hereinafter, it will be appreciated that the present invention provides a means for accurately locating and measuring the emissions from a source of radiation such as a body abnormality. The apparatus of this invention is believed to increase the percentage of positive detection of abnormalities relative to either the ultrasound or the radiation detecting methods of the prior art. Moreover, a surgical procedure is not required. Other advantages and novel features will be apparent in view of the following detailed description of the preferred embodiment.